Field of the Invention
The present invention relates to a light distribution characteristic measurement apparatus and a light distribution characteristic measurement method of measuring the light distribution characteristic of a light source.
Description of the Background Art
The light distribution characteristic is known as one of the characteristics of light emitted from a light source. The light distribution characteristic means a spatial distribution of the luminous intensity (or luminance) of a light source. As the light distribution characteristic, both the absolute-value-based light distribution and the relative-value-based light distribution are used. The absolute-value-based light distribution is a measurement of the spatial distribution of the absolute value of the luminous intensity and is used in such a case where the total luminous flux generated by a light source is to be determined. In contrast, the relative-value-based light distribution is a measurement of the spatial distribution of the relative value of the luminous intensity, and is used in such a case where the light distribution pattern is to be determined. Generally, it is not easy to measure the light distribution characteristic of light sources such as a light source having a complicated light distribution pattern and a light source whose characteristics are not known.
Regarding such measurement of the light distribution, Japanese Patent Laying-Open No. 2013-217651 discloses a light distribution characteristic measurement apparatus capable of efficiently measuring the light distribution characteristic of a light source without increase of the apparatus configuration.
In the case where the light distribution characteristic measurement apparatus disclosed in Japanese Patent Laying-Open No. 2013-217651 is used to measure the surface luminance of a light source, the light distribution characteristic can be measured with a desired precision if the area of a light-emitting portion (bright portion) of the light source to be measured is relatively large and the luminance of the light-emitting portion is measured.
In the case for example where a light source with a strong directivity like headlight of an automobile is to be measured, there is a large difference in luminance between a light-emitting portion (bright portion) and a non-light-emitting portion (dark portion) and therefore, it is not easy to stably measure the luminance of the non-light-emitting portion.